Long Term Evolution (LTE) supports data rates up to 100 Mbps in the downlink and 50 Mbps in the uplink. LTE-Advanced (LTE-A) provides a fivefold improvement in downlink data rates relative to LTE using, among other techniques, carrier aggregation. Carrier aggregation may support, for example, flexible bandwidth assignments up to 100 MHz. Carriers are known as component carriers in LTE-A. A wireless transmit/receive unit (WTRU) may simultaneously receive one or more component carriers.
LTE-A may operate in symmetric and asymmetric configurations with respect to component carrier size and the number of component carriers. This is supported through the use or aggregation of up to five 20 MHz component carriers. For example, a single contiguous downlink (DL) 40 MHz LTE-A aggregation of multiple component carriers may be paired with a single 15 MHz uplink (UL) component carrier. Non-contiguous LTE-A DL aggregate carrier assignments may therefore not correspond with an UL aggregate carrier grant.
Aggregate carrier bandwidth may be contiguous where multiple adjacent component carriers may occupy continuous 10, 40 or 60 MHz. Aggregate carrier bandwidth may also be non-contiguous where one aggregate carrier may be built from more than one, but not necessarily adjacent component carriers. For example, a first DL component carrier of 15 MHz may be aggregated with a second non-adjacent DL component carrier of 10 MHz, yielding an overall 25 MHz aggregate bandwidth for LTE-A. Moreover, component carriers may be situated at varying pairing distances. For example, the 15 and 10 MHz component carriers may be separated by 30 MHz, or in another setting, by only 20 MHz. As such, the number, size and continuity of component carriers may be different in the UL and DL.
In LTE, WTRUs receive their data (and in some cases their control information) on the physical downlink shared channel (PDSCH). The transmission of the PDSCH is scheduled and controlled by the base station using the so-called downlink scheduling assignment, which is carried on physical downlink control channel (PDCCH). As part of the downlink scheduling assignment, the WTRU receives control information on the modulation and coding set (MCS), downlink resources allocation (i.e., the indices of allocated resource blocks), and other similar information. Then, if a scheduling assignment is received, the WTRU will decode its allocated PDSCH resources on the correspondingly allocated downlink resources.
In LTE-A, PDSCH(s) to a given WTRU may be transmitted on more than one assigned component carrier and multiple approaches for allocating PDSCH resources on more than one component carrier may exist.
In LTE-A, the PDCCHs or Downlink Control Information (DCI) messages contained therein carrying the assignment information may be separately transmitted for the component carriers containing the accompanying PDSCH transmissions. For example, if there are 2 component carriers, there are 2 separate DCI messages on each component carrier corresponding to the PDSCH transmissions on each component carrier respectively. Alternatively, the 2 separate DCI messages for the WTRU may be sent on one component carrier, even though they may pertain to accompanying data, or PDSCH transmissions on different component carriers. The separate DCI messages of the PDCCHs for a WTRU or a group of WTRUs may be transmitted in one or in multiple component carriers, and may not transmit all of the PDCCHs on every component carrier. For example, a first DCI transmission on the PDCCH pertaining to the PDSCH allocation on a first component carrier may also be contained on this first component carrier, but the second DCI to that WTRU PDCCH transmission pertaining to the PDSCH allocation on a second component carrier may be contained on this second component carrier.
The DCI carrying the assignment information for PDSCH(s) on more than one component carrier may be encoded jointly and carried by one single joint DCI control message, or PDCCH message. For example, a single DCI or PDCCH or control message carrying an assignment of PDSCHs or data resources on two component carriers may be received by the WTRU. In another example, the joint PDCCH for a WTRU or group of WTRUs may be transmitted in one or multiple component carriers.
In LTE-A with carrier aggregation, different PDCCH assignments, coding or allocation schemes represent distinct technical advantages. Both UL grants and DL assignments may be carried by PDCCHs. Due to asymmetric carrier aggregation, PDCCH methods that may be suitable for DL assignments may not be suitable for UL grants. Furthermore, PDCCH methods that are suitable for some configurations or assignments/grants of carrier aggregation may not be suitable for other configurations or assignments/grants of carrier aggregation. For example, in an asymmetric carrier aggregation in which there are more UL component carriers than DL component carriers, a separate PDCCH may be directly used for DL assignment because there exists one-to-one mapping between a DL carrier and the DL carrier that transmits the DL assignment. In other words, a DL assignment that may be transmitted in DL component carrier x carries control information for DL component carrier x. However, in this case separate PDCCH may not be directly used for UL grants because there are more UL component carriers than DL component carriers. This is also true in the case of asymmetric carrier aggregation where more DL component carriers than UL component carriers are used. In addition, when different encoding and transmission schemes are used, how UL grants are mapped to UL component carriers and DL assignments to DL component carriers should be specified.
Methods to associate or map the DL assignment to DL component carrier and UL grant to UL component carrier are desired. This may be particularly true when asymmetric carrier aggregation, UL grants and different encoding/transmission schemes are considered. Optimal methods that are suitable for separate or joint DL assignments and UL grants are desirable.